An Otago University scientist may have unravelled a 2,000-year-old mystery of what killed Alexander the Great.

National Poisons Centre toxicologist Dr Leo Schep thinks the culprit could be poisonous wine made from an innocuous-looking plant.

Classical scholars have been deeply divided about what killed the Macedonian leader, who built a massive empire before his death, aged 32, in June of 323BC. Some accounts say he died of natural causes but others suggested members of his inner circle conspired to poison him at a celebratory banquet.